Harness High-Temperature Thermal Energy via Elastic Thermoelectric Aerogels

Highlights A thermoelectric aerogel of highly elastic, flame-retardant and high-temperature-resistant PEDOT:PSS/SWCNT composite is fabricated. The assembled thermoelectric generator generates a maximum output power of 400 μW at a temperature difference of 300 K. The self-powered wearable sensing glove can achieve wide-range temperature detection, complex hand motion recognition and high-temperature warning. The intelligent fire warning system enables highly sensitive and repeatable monitoring and alarm capabilities for high-temperature fire sources. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-024-01370-z.

Fig. S1 Digital photos of the state of composite aerogel with and without PEDOT:PSS before and after compression Figure S1 illustrates that the absence of PEDOT:PSS resulted in an aerogel that could not fully recover its original state after compression, indicating insufficient resilience.PEDOT:PSS plays a crucial role in the mechanical (elastic) and TE properties of the PEDOT:PSS /SWCNT composite aerogel.On one hand, the presence of PSS (polystyrene sulfonic acid) in PEDOT:PSS interacts with crosslinkers (3-glycidyloxypropyltrimethoxysilane, GOPS) and a small amount of carboxymethyl nanocellulose, which contributes to the improvement of mechanical properties.On the other hand, there is also a π-π interaction between the PEDOT molecular chain and SWCNT, promoting the enhancement of both TE and mechanical properties.The thermal conductivity (κ) of the aerogel was measured using the Hot Disk thermal constant analyzer (Hot Disk TPS3500) based on the principle of transient plane source method.The testing process is illustrated in Fig. S5, where two aerogel samples with dimensions of approximately 15 mm × 15 mm × 10 mm (length × width × height) were tested for thermal conductivity in original state (without compression) and compressed state (50% compression).The probe is sandwiched between the two samples to form a sandwich structure for thermal conductivity testing (each state is tested twice to verify the accuracy of the results).
The testing results are presented in Table S2, and a screenshot of the testing results is shown in Fig. S6.This testing method provides information on thermal diffusion coefficient (α) and volumetric heat capacity (cv).By measuring the mass and volume of the samples, the density (ρ) can be calculated.Finally, using the formula κ = ρ × cv × α, the thermal conductivity κ of the aerogel can be determined.Various hand gestures Fig. S12 Photographs showing the hand gestures of "Spread", "Point", "Pinch" and "Grip" when wearing the integrated aerogel-based sensor glove

Hand motion recognition
The integrated thermoelectric (TE) sensing glove can be used to hand motion recognition.It is well-known that the TE sensing glove, when in contact with an object, generate a voltage signal that is highly dependent on the temperature difference (ΔT) between the object and human finger heat.
Specially, three characteristic voltage signals (Knuckle 1, Knuckle 2 and Knuckle 9) are collected to elucidate the application of the integrated TE sensing glove for hand motion recognition (such as spread, point, pinch, and grip).Distinct voltage amplitudes in the three knuckle sensors enable the recognition of hand gestures.The "Spread" pattern is characterized by the relatively similar voltage amplitude in all three knuckles.The "Point" pattern is characterized by a high voltage amplitude in Knuckles 2 and low voltage amplitudes in Knuckle 1 and Knuckle 9.The "Pinch" pattern is characterized by a high voltage amplitude in Knuckle 1 and Knuckle 2, and a low voltage amplitude in Knuckle 9.The "Grip" pattern is characterized by a high voltage amplitude in Knuckle 2 and Knuckle 9, and a low voltage amplitude in Knuckle 1.It should be noted that the voltage amplitude is nearly same when applying the same ΔT.
Nano-Micro Letters S8/S17 Herein, three voltage parameters are distinguished in the recognition tests: the measured voltage amplitude (VX), the maximum voltage (Vmax), and the threshold voltage (VtX).Vmax refers to the highest voltage generated by the sensor under a certain temperature difference.VtX is defined as a characteristic voltage for recognizing gestures, it can be calculated by Equation VtX = kVmax, where subscript X represents the sensor name corresponding to the knuckle order (Fig. 5a), and k is the ratio of VtX to Vmax and can be adjusted artificially.For instance, Vt1 represents the threshold voltage of Knuckle 1.The optimal k value is determined by recognition experiment.The intelligent fire warning system Fig.S16 The designed self-powered smart fire warning system

TE properties of composite aerogels with different PEDOT:PSS contents
Table S1 The TE properties of various PEDOT/SWCNT composite aerogels with different PEDOT:PSS contents Firstly, the content of SWCNT (136 mg) is fixed, and the content of NFC (15 mg) is determined to ensure the dispersion of SWCNT.The ratio of NFC to the crosslinker GOPS is  also fixed (NFC:GOPS = 1:10).The optimal mass ratio of PEDOT:PSS to SWCNT in composite aerogels was determined based on the desired mechanical and TE properties of the resulting aerogels, aiming to achieve excellent elasticity and TE performance.Table S1 presents the results, it can be seen that a high PEDOT:PSS content significantly reduced the power factor (PF) of the composite aerogel, impacting its electrical conductivity (σ) or Seebeck coefficient (S).This is because the commercially PEDOT:PSS aqueous solution itself exhibits lower TE performance (σ = 0.1 S cm −1 , S = 15.5 μV K −1 ).In this study, we did not carry out any additional performance modifications on PEDOT:PSS.Thus, a high PEDOT:PSS content would diminish the TE properties of the composite aerogel.Therefore, the optimal weight ratio of PEDOT:PSS to SWCNTs is 15:136.Combining the above points, the final optimal weight ratio of PEDOT:PSS:SWCNT:NFC:GOPS = 15:136:15:150.

Nano
Fig. S2 Photographs showing the specific-sized PTFE molds: a Diameter is 7 mm and height is 5 mm.b Diameter is 7 mm and height is 10 mm Self-established apparatus

Fig. S6
Fig. S6 Screenshots of thermal conductivity test results

Fig. S13
Fig. S13 The algorithm logic diagram in hand motions recognition experiment

Fig. S14
Fig. S14 The voltage amplitudes generated in three knuckles (knuckle 1, 2 and 9) during a series of random hand motions.The green dash line represents the "threshold voltage" with a k value of 0.55 in the recognition experiment Based on previous empirical values [39], setting k is 0.55, the voltage amplitude variations at the three Knuckles are shown in Fig. S14.It can be observed that the hand gestures of "Point," "Pinch," and "Grip" exhibit distinct changes near the threshold voltage (VtX), indicating its effective hand motions recognition capability.

Table S2
Thermal conductivity parameters obtained from tests of PEDOT/SWCNT composite aerogels in the original and compression states

Table S3
Comparison of the TE performance of various polymer or polymer/carbon nanoparticle composite aerogels

Output performance comparison of the aerogel-based TE generatorsTable S4
Comparison of the output performance of aerogel-based TE generators